A powder bed ALM process starts with a bed of powdered material such as a ceramic, a ferrous alloy or a non-ferrous alloy. Regions within the powder mass are selectively treated, for example by melting or sintering, to solidify. The untreated powder remains in a layer as the next layer is formed. Surplus (untreated) material may be removed when the three dimensional build is complete and can be recycled.
The nature of powder bed ALM permits that a component can be constructed from multiple powdered materials, however, this is not currently a practical option. Firstly, the changeover of a powder type inside an ALM machine is a lengthy processes adding to the overall cost of the component manufacture. Secondly, since the addition of a second powder contaminates a first powder, re-cycling of any untreated powders is near impossible. Materials used are a high value commodity and wastage is desirably minimised. As a consequence powder bed ALM parts are currently engineered to be built in a single material.